Method for demonstrating breathability

ABSTRACT

A method for demonstrating breathability by providing an aliquot of liquid in a container having an opening; forming a closed system by securing a film about the opening; imparting evaporation on the closed system; and measuring or observing the remaining fluid after a predetermined time.

This application claims benefit of Provisional No. 60/242,553 filed Oct.23, 2000.

This invention relates to a method for demonstrating breathability of anabsorbent article or a film using a closed system.

BACKGROUND OF THE INVENTION

Absorbent articles receive body exudates, including fluids and solids.Absorbent articles function both to contain the discharged materials andto isolate these materials from the body of the wearer and from thewearer's garments and the environment. Absorbent articles having manydifferent basic designs are known and include diapers, sanitary napkins,pantiliners, and wound care articles, including surgical dressings andadhesive bandages.

Typically, an absorbent article has three major components: a top sheet,an outer backsheet, and an absorbent core therebeteween. In normal use,the top sheet contacts the wearer's skin and provides channels totransport body fluids to the absorbent core. The absorbent corefunctions to retain the body exudates. The backsheet contacts thewearers' clothing or garment and is typically a flexible, fluid andvapor impervious sheet that prevents absorbed fluid from soiling thewearer's clothing, bedding, and the like.

Specifically, the backsheet is often constructed from fluid imperviousfilms, such as those made from polyolefins, e.g., polyethylene andpolypropylene. Although such backsheets do prevent fluid from passingthrough the absorbent article, they also can make the wearer of theabsorbent article uncomfortable due to their impermeability to airand/or moisture vapor. Surprisingly, it has been found that amicroporous film having a low basis weight and high MVTR values can beused in a variety of absorbent articles to increase the wearer's comfortand promote skin and body wellness.

SUMMARY OF THE INVENTION

A method for demonstrating breathability by providing an aliquot ofliquid in a container having an opening; forming a closed system bysecuring a film about the opening; imparting evaporation on the closedsystem; and measuring or observing the remaining fluid after apredetermined time is disclosed.

DETAILED DESCRIPTION OF THE INVENTION

The absorbent articles of this invention, include, but are not limitedto disposable diapers, sanitary napkins, tampons, pantiliners, woundcare articles, including surgical dressing and adhesive bandages, andthe like.

As used herein, terms such as “less than,” “or less,” “greater than,”“or greater,” and the like are intended to include disclosure of allnumbers not expressly recited. For example, a recitation of “100 orless” is intended to include an express disclosure of, for example, 24,33, 45.01, 67.499922, 1, 0.002352, 99.9999999, 100, and the like.

As is well known to those skilled in the art, absorbent articles thatare worn externally generally have a layered construction with abody-facing surface that is oriented to face the wearer during use and agarment-facing surface oriented in the opposite direction from thebody-facing surface. Typically, such articles have a liquid perviouscover on the body-facing surface of the article, an absorbent core, anda backsheet on the garment-facing surface of the article. The absorbentcore is interposed between the cover and the backsheet. The cover andthe backsheet encase all components of the article. The cover and thebacksheet are joined or sealed to each other along their peripheral edgeusing methods described below. Additional components that also extend tothe peripheral edge of the article can be also joined or sealed to theperipheral edge of the cover and/or backsheet. These peripheral joindersdo not replace the adhesive attachments within the article.

In accordance with an embodiment of the present invention, there isprovided a novel absorbent article, having a body-facing fluid permeablecover sheet, a fluid impermeable backsheet, which in the case ofsanitary products face the users garment when in use, and an absorbentcore between the cover sheet and the backsheet.

The liquid permeable cover of the absorbent article may be formed fromany fluid pervious material that is comfortable against the skin andpermits fluid to penetrate to the absorbent core. The cover shouldretain little or no fluid in its structure in order to provide arelatively dry surface next to the skin. The cover may be a fibrousfabric made of fibers, including bicomponent fibers, or filaments ofpolymers, such as polyethylene, polypropylene, polyester, or cellulose.Alternatively, the cover may be formed from an apertured film, plasticnets, webs, and the like. Any of these materials may be used.

In an embodiment, the cover is a non-woven fabric formed from aninterconnected network thermoplastic polymer fibers, at least a portionof the non-woven fabric having a three-dimensional thickness profilehaving a plurality of raised regions, semi-raised regions, andcompressed regions. The raised regions having a lower fiber densityrelative to the semi-raised regions and the semi-raised regions having alower fiber density relative to the compressed regions. See, forexample, U.S. Pat. No. 6,087,551, which is incorporated herein byreference in its entirety.

The absorbent core can be a fluffy batt cut from a relatively loose webof non-woven fibers having a relatively high absorptive capacity. Theabsorbent core usually has a rectangular configuration, and mayoptionally have inwardly curved side edges, such as an hourglass shape.The absorbent core is usually smaller than the backing sheet and thecover. The absorbent core may also be a fibrous batt having an integraldensified layer. In such a case, the absorbent core is positioned on thebacking sheet of the absorbent article so that the densified layeradjoins the backing sheet. The densified layer has relatively higherwettability and liquid retentivity than the rest of the aforesaid battand usually is formed by slightly moistening one surface of the batt andthereafter compressing the moistened surface.

The absorbent core may contain any material that absorbs bodilysecretions including, but not limited to pulp, polymeric fibers andfilaments, spagnum moss, natural fibers, superabsorbent polymers(including fibers, particulate material, and foams), absorbent foams,and other such absorbent materials. The absorbent core is cellulosicfibers and superabsorbent polymer particles. The absorbent core may alsoinclude additional materials, such as odor control material, wetnessindicator material, materials for administering or deliveringmedicaments, such as encapsulated medicaments, and materials formaintaining skin moisture, such as encapsulated moisturizers.

The cover and backsheet are usually substantially coextensive and arejoined together about the periphery of the absorbent article.Additionally, the absorbent core may be anchored to the cover, thebacksheet, or other components of the absorbent article. Methods forattaching the components together are included in the discussion ofadhesives.

The backsheet may be of any flexible material that prevents the transferof fluid through it, but, does not necessarily prevent the passages ofgases. Backsheets that are pervious to vapor are known as breathablebacksheets. In general, these backsheets are intended to allow thepassage of vapor through them while retarding, at least to a degree, thepassage of fluid. Porous film technology provides materials that can beused to form sheets that allow vapor transmission, but are relativelyimpervious to liquids. Commonly used materials are polyethylene orpolypropylene films. Other materials that may be used as impermeablebarriers may be chosen from films of polyesters, polyamides,polyethylene vinyl acetate, polyvinyl chloride, and polyvinylidenechloride. Co-extruded and laminated combinations of the foregoing,wherein such combinations are permitted by the chemical and physicalproperties of the film, may be used. Fluid impermeable nonreticulatedfoams and repellent treated papers may also be used. Films that arefluid barriers, but permit gases to transpire, i.e., “breathable films,”may also be used. These include in particular, porous or microporousfilms, as previously described. The gasses most commonly used todemonstrate a film's breathability are water vapor, sometimes referredto as moisture vapor, and oxygen.

The moisture vapor transmission rate test (“MVTR”) measures the mass orvolume of gas transported across the cross section of the film in agiven unit of time at a defined set of environmental conditions. Whilethe mechanism of gas transfer often differs from film to film, it is thetotal amount of gas that passes through the film that makes filmsbreathable.

When in close proximity to the skin, high MVTR films allow the body tocool itself naturally, e.g., excess moisture to evaporate. When a highMVTR film also provides a barrier to liquid transfer and/or microbialtransfer, there are a variety of applications, most of which are indirect or indirect contact with skin, that can take advantage of thisunique combination of properties.

A suitable backsheet material can be a microporous sheet made frompolyolefin or blends thereof. In an embodiment, the backsheet is amicroporous sheet made from a blend of a linear low-densitypolyethylene, a low density polyethylene, and a calcium carbonatefiller. Additionally, other components, such as antioxidants andpigments, may be added to the blend.

In particular, microporous films have been made by incorporating fillerparticles into a polymer and stretching the resulting material to form afilm having voids induced by the filler particles. Incorporating fillerparticles into a polymer introduces a range of variables forconsideration. Such variables include the type of filler, the amount offiller, the filler particle size and size distribution,surface-modifications of the filler particles, the mode or method ofstretching the film, and the like. Each of these variables can affectthe morphology and properties of the resulting film.

In the process of making the film, the components are blended, extruded,and embossed. The resultant film can then be stretched and heat-cured.Such methods are known, see for example, U.S. Pat. No. 4,777,073, whichis incorporated herein by reference in its entirety. A film madeaccording to the above methodology, as used in the present invention, isa single layer film having a low basis weight, a high breathability, andis heat sealable.

In particular, the breathable film used in the present invention has abasis weight of about 32 g/m² or less, about 30 g/m² or less, or about28-30 g/m². In addition, the film used in the present invention also hasan MVTR of from about 5800 to about 10000 g/m²/24 hrs, from about 5900to about 6300 g/m²/24 hrs, or about 6000 g/m²24 hrs.

Porous films include a first major length-wise dimension or direction,and a second major, generally cross-wise dimension or direction that issubstantially perpendicular to the first dimension. Porous films alsohave a third dimension or direction that extends along the bulkthickness of the film and is substantially perpendicular to both thefirst and second major directions.

The backsheet may be fixed or otherwise adhered to the surface of theabsorbent core overall or in discrete zones of attachment. The backsheetmay be adhered to the cover in an overlapping configuration, forexample, parallel to the sides of the absorbent structure, parallel tothe bottom of the absorbent article, or in a flange seal extending fromthe sides of the absorbent structure. When the cover and backsheet areadhered to each other in a flange seal, the cover may additionally bewrapped around the flange seal about the cover; or the backsheet mayadditionally be wrapped around the flange seal about the cover.

The absorbent article may optionally have a multi-layered structure thatmay additionally contain a transfer layer, which is a low density fluidaccepting and fluid releasing layer, that is usually located between thecover and the absorbent core. The transfer layer may be made ofrelatively less hydrophilic materials and structures than is containedin the absorbent core, such as of webs of meltblown polypropylene orpolyester fibers. Such webs may also contain woodpulp entrained within.Transfer layers may also be made of low density, highloft nonwoven webof woodpulp and synthetic fibers, such as polyethylene, polypropylene,polyester, polyacrylonitrile, and polyamide. Such highloft webs may bebonded with chemical binders or by thermal means, such as by through-airbonding.

The layers of the article may be attached or adhered to one another toform a cohesive unit to enhance the article's stability. Such attachmentor adherence may be by any known means, including, for example,adhesive, ultrasonics, co-embossing, thermobonding, mechanical bonding,and the like. However, the adhesive does not inhibit the vaportransmission or breathability of the backsheet. In the case of apantiliner, a construction adhesive is present between the cover and theabsorbent core and also present between the absorbent core and thebacksheet. The construction adhesive serves to hold the layers togetherand to minimize deformation during use. The adhesive can be applied aseither a thin porous film or in a random spray, in a controlled spiralpattern, or in any other application pattern. See, for example, U.S.Pat. Nos. 5,462,538; 5,681,305; and 5,885,681, the disclosures of whichare herein incorporated by reference in their entirety.

The absorbent article, in the case of a sanitary napkin or pantiliner,may be applied to the crotch of underpants by placing the backsheet ofthe absorbent article against the inside of the crotch of theunderpants. Pressure sensitive adhesive may be applied to the outersurface backsheet of the absorbent article to help maintain it in place.As used herein, the term “pressure-sensitive adhesive” refers to anyreleasable adhesive or releasable tenacious means. Suitable pressuresensitive adhesives include, for example, water-based adhesives, such asacrylate adhesives. Alternatively, the adhesive may be a rapid settingthermoplastic “hot melt” rubber adhesive or two-sided adhesive tape.

A paper release strip that has been coated on one side, may be appliedto protect the adhesive on the backsheet prior to use. The coating onthe release paper, for example, silicone, reduces adherence of thecoated side of the release to the backsheet adhesive. The release stripcan be formed from any suitable sheet-like material that, when coated,adheres with sufficient tenacity to the adhesive to remain in placeprior to use, but can be readily removed when the absorbent articleprior to placement on the wearer's underpants.

The absorbent articles of the present invention can be of various shapesand configurations depending on the intended end use, e.g., asdisposable diapers, sanitary napkins, pantiliners, tampons, underpads,surgical dressings or wipes, and the like. Additionally, the presentabsorbent articles can be incorporated into a disposable or limited usegarment as an integral part thereof. For example, an absorbent articlemade according to the present invention can be a part of disposabletraining pants and similar garments.

The thickness of the absorbent core may be uniform throughout theexpanse of the absorbent element or, for the purpose of specific fit,flexibility, and absorbency requirements, the absorbent core may bethicker in some regions than in others. For example, a embodiment hasthickness profile wherein an absorbent core is thicker in the centralregion than it is in the end regions. Additionally, while any thicknessof absorbent core is contemplated to be used in the instant invention,an embodiment includes an absorbent core that is thin, i.e., having acaliper thickness of less than about 5 mm, less than about 3.5 mm, orless than about 2.3 mm.

Any or all of the cover, absorbent core, transfer layer, backsheet, andadhesive may be colored. Such coloring includes, but is not limited to,white, black, yellow, blue, orange, green, violet, combinations thereof,and the like. Color may be imparted according the present inventionthough printing, dying, pigmentation, and/or filler particles. Colorantsused according the present invention include dyes and inorganic andorganic pigments. The dyes include, but are not limited to, Azo dyes(e.g., Solvent Yellow 14, Disperse Yellow 23, Metanil Yellow),anthraquinone dyes (Solvent Red 111, Disperse Violet 1, Solvent Blue 56,and Solvent Green 3), Xanthene dyes (Solvent Green 4, Acid Red 52, BasicRed 1, and Solvent Orange 63), azine dyes (Jet black), and the like.

Inorganic pigments include, but are not limited to, titanium dioxide(white), carbon black (black), iron oxides (red, yellow, and brown),chromium oxide (green), ferric ammonium ferrocyanide (blue), and thelike.

Organic pigments include, but are not limited to diarylide yellow AAOA(Pigment Yellow 12), diarylide yellow AAOT (Pigment Yellow 14),phthalocyanine blue (Pigment Blue 15), lithol red (Pigment Red 49:1),Red Lake C (Pigment Red), and the like.

Absorbent articles within the scope of this invention also include woundcare articles such as bandages, including adhesive bandages. Adhesivebandages usually have a backsheet of perforated plastic or of a woven orknit fabric. The backsheet is covered completely or partially on oneside with a pressure sensitive adhesive. An absorbent core is placed inthe center of and adhered to the adhesive side of the backing material.The absorbent core typically lies between a cover, which contacts theskin and prevents the absorbent from sticking to the wound, and thebacksheet.

In the description above and in the following non-limiting examples, thefollowing methods were employed to determine various reportedcharacteristics and properties.

The basis weight was reported by the manufacturer as being 30 g/m².

MVTR was determined by the following method: an environmental chamberwas provided and maintained at 37 +/−1° C. and a relative humidity of˜10%. Film samples were then preconditioned in the environmental chamberto maintain moisture levels. 10 ml of DI water as added to a Payne Cup,e.g., a metal cup with an exposed surface of 10 cm. A preconditionedfilm sample was place over the flange of the cup. The sample was thenclamped or sealed to the Payne Cup. The Payne Cup with sample wasweighed. After weighing, the Payne Cup with sample were placed in theenvironmental chamber, which was maintained at 37° C. and 10% RH. After24 hours, the Payne Cup with sample were allowed to cool to roomtemperature. After cooling, the Payne Cup with sample were reweighed.MVTR was calculated using the following formula: Initial Weight−FinalWeight*1000=MVTR.

The breathability of the material chosen as a backsheet may also bedemonstrated using the Lost Fluid Dynamic Test (“LFDT”).

In the LFDT, at least two fluid containing devices, such as beakers,closed funnels, test tubes, and the like are supported over heatingelements, such as a hotplate. An equal aloquoit of fluid is added toeach device, the fluid having a viscosity similar to biological saline.The edges of the film were sealed about the opening each device, therebyforming closed systems. The closed system was exposed to elevatedtemperatures, e.g., about 37° C., for a predetermined time, e.g., about4 to about 6 hrs, or about 5.5 hrs. The closed systems of the LFDT wereremoved from the heat source and evaluated for the loss of liquid.Visual observations for the loss of liquid included reduction of thefluid level in the container and presence of condensation on the innersurface of the film. Additional quantitative methods included weighingfluid before and after exposure to heat to indicate how much fluid haspassed through the film.

The following table provides the results of one such test.

Initial Fluid Weight Final Fluid Weight Beaker Number (g.) (g.) % Loss 15.2 1.51 71.0 2 (comparative) 5.2 5.07  2.5

From the above table, beaker 1 demonstrates a significant loss of fluidthrough the backsheet film, whereas there is minimal fluid loss inbeaker 2. While all films, regardless of their breathability, allow somevapor transmission through the film, the difference of more than 68% inthe LFDT demonstrated above over a 5.5 hour period is consideredsignificant.

The above test can be captured or recorded graphically or pictorally anddisplayed to a wearer to educate the consumer about breathability, amongother things.

The foregoing description is intended as illustrative and are not to betaken as limiting. Still other variations are possible without departingfrom the spirit and scope of this invention and will readily presentthemselves to one skilled in the art.

We claim:
 1. A method for demonstrating breathability comprising: a) providing an aliquot of fluid in a container having an opening; b) forming a closed system by securing a film about the opening; c) imparting evaporation on the closed system by heating the closed system to an elevated temperature for a first predetermined time; d) returning the temperature of the closed system to the temperature of the closed system prior to heating the closed system: and e) measuring or observing the remaining fluid after a second predetermined time.
 2. A method for demonstrating breathability of claim 1, wherein the closed system is heated to about 37° C.
 3. A method for demonstrating breathability of claim 2, wherein the first predetermined time is from about 4 to about 6 hours.
 4. A method for demonstrating breathability of claim 3, wherein the first predetermined time is about 5.5 hours.
 5. A method for demonstrating breathability of claim 1, wherein at least two films are compared.
 6. A method for demonstrating breathability of claim 5, wherein at least one film is non-breathable.
 7. A method for demonstrating breathability of claim 6, wherein at least one film is breathable.
 8. A method for demonstrating breathability of claim 5, wherein at least one film is breathable.
 9. A method for demonstrating breathability of claim 8, wherein at least one film is non-breathable.
 10. A method for demonstrating breathability of claim 8, wherein the measurement or observation is recorded graphically or pictorally.
 11. A method for demonstrating breathability of claim 10, wherein the graphic or picture is conveyed on a computer, television, or paper.
 12. A method for demonstrating breathability of claim 1, wherein the measurement or observation is recorded graphically or pictorally.
 13. A method for demonstrating breathability of claim 12, wherein the graphic or picture is conveyed on a computer, television, or paper.
 14. A method for demonstrating breathability comprising: a) providing an aliquot of liquid in a container having an opening; b) forming a closed system by securing at least part of an absorbent article about the opening; c) imparting evaporation on the closed system by heating the closed system to an elevated temperature for a first predetermined time; d) returning the temperature of the closed system to the temperature of the closed system prior to heating the closed system; and e) measuring or observing the remaining fluid after a second predetermined time.
 15. A method for demonstrating breathability of claim 14, wherein the closed system is heated to about 37° C.
 16. A method for demonstrating breathability of claim 15, wherein the predetermined time is from about 4 to about 6 hours.
 17. A method for demonstrating breathability of claim 16, wherein the predetermined time is about 5.5 hours.
 18. A method for demonstrating breathability of claim 14, wherein at least two absorbent articles are compared.
 19. A method for demonstrating breathability of claim 18, wherein at least one absorbent article is non-breathable.
 20. A method for demonstrating breathability of claim 18, wherein at least one absorbent article is breathable.
 21. A method for demonstrating breathability of claim 14, wherein the measurement or observation is recorded graphically or pictorally.
 22. A method for demonstrating breathability of claim 21, wherein the graphic or picture is conveyed on a computer, television, or paper.
 23. A method for demonstrating breathability comprising: a) providing an aliquot of liquid in a container having an opening; b) forming a closed system by securing a film about the opening; c) imparting evaporation by heating the closed system to about 37° C. for about 5 to about 6 hours; d) returning the temperature of the closed system to the temperature of the closed system prior to heating the closed system; and e) measuring or observing the remaining fluid after a predetermined time.
 24. A method for demonstrating breathability of claim 23, wherein the closed system is heated for about 5.5 hours. 